1. Technical Field
The present invention relates to a measurement apparatus, a measurement method, and a test apparatus. In particular, the present invention relates to a measurement apparatus, a measurement method, and a test apparatus for measuring a time between change points, i.e. edges, of a signal under measurement.
2. Related Art
Japanese Patent Application Publication No. 6-94853 discloses a time measurement circuit that measures the timings of pulse edges. This time measurement circuit includes a counter that counts a clock, a latch that latches a value of the counter, a triangular wave generating circuit that generates a triangular wave in synchronization with the clock, an AD converter, and an adding device.
The latch acquires the counter value at the edges of the pulse under measurement. The AD converter samples the level of the triangular wave the edges of the pulse under measurement. The adding device outputs the edge timing of the pulse under measurement obtained by adding together the count value acquired by the latch and the output data of the AD converter. This time measurement circuit can accurately measure the edge timing of the pulse under measurement in less than one cycle of the clock.
When measuring a short pulse width that is only a few nanoseconds, the time measurement circuit must be provided with a high-speed AD converter to continuously sample the pulse at short intervals. Such a high-speed AD converter, however, is expensive and has relatively low accuracy.